In many applications, it is necessary to verify the identity of an unknown person. One example of an identity verification device is a photo badge by which an interested party may compare the photo on the badge with the person claiming an identity in order to verify the claim. This method of verification has many shortcomings. Badges are prone to loss and theft, and relatively easy duplication or adulteration. Furthermore, the inspection of the badge must be performed by a person, and is thus not applicable to many situations where the verification must be done by a machine. In short, an effective verification system or device must be cost-effective, fast, accurate, easy to use and resistant to tampering or impersonation.
Long distance credit card services, for example, must identify a user to ensure that an impostor does not use the service under another person's identity. Prior art systems provide a lengthy identification number (calling card number) which must be entered via the phone's keypad to initiate the long distance service. This approach is prone to abuse, since the identification number may be easily appropriated by theft, or by simply observing the entry of the identification number by another. It has been estimated that the loss to the long distance services due to unauthorized use exceeds $500,000,000 per year.
Speaker verification systems have been available for several years. However, most applications require a very small true speaker rejection rate, and a small impostor acceptance rate. If the true speaker rejection rate is too high, then the verification system will place a burden on the users. If the impostor acceptance rate is too high, then the verification system may not be of value. Prior art speaker verification systems have not provided the necessary discrimination between true speakers and impostors to be commercially acceptable in applications where the speaking environment is unfavorable.
Speaker verification over long distance telephone networks present challenges not previously overcome. Variations in handset microphones result in severe mismatches between speech data collected from different handsets for the same speaker. Further, the telephone channels introduce signal distortions which reduce the accuracy of the speaker verification system. Also, there is little control over the speaker or speaking conditions.
Therefore, a need has arisen in the industry for a system to prevent calling card abuse over telephone lines. Further, a need has arisen to provide a speaker verification system which effectively discriminates between true speakers and impostors, particularly in a setting where verification occurs over a long distance network.